Network utilities in wireless mesh communications networks

ABSTRACT

Methods and systems for providing a network and routing protocol for utility services are disclosed. A method includes discovering a utility network. Neighboring nodes are discovered and the node listens for advertised routes for networks from the neighbors. The node is then registered with one or more utility networks, receiving a unique address for each network registration. Each upstream node can independently make forwarding decisions on both upstream and downstream packets, i.e., choose the next hop according to the best information available to it. The node can sense transient link problems, outage problems and traffic characteristics. Information is used to find the best route out of and within each network. Each network node maintains multi-egress, multi-ingress network routing options both for itself and the node(s) associated with it. The node is capable of several route maintenance functions utilizing the basic routing protocol and algorithms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/818,887, filed Jun. 15, 2007, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND

The subject matter presented herein relates generally to networks andnetwork-based computer systems, and more particularly to methods andsystems for providing network and routing protocols for utility and homearea services.

SUMMARY

The exemplary embodiments illustrate a routing scheme and protocols inan RF network (terrestrial or wireless LAN) operating in FHSS mode toenable two-way communications between a utility and home devices (suchas electric meters, water meters, gas meters, Distribution Automation(DA) devices, and in-premise devices) that are IP hosts in the RF LANnetwork, interconnecting with the Utility Host System (also referred toas Back Office Server or BOS) which is an IP host in a wireless or wiredWAN (Wide Area Network) infrastructure. The IP version in the exemplaryembodiment is IPv6. When traversing a typical IPv4 WAN cloud, the IPv6packets are encapsulated in IPv4 for transmission. The method forrouting IPv6 packets in the wireless LAN network includes providing aGateway that can perform encapsulation (e.g., of IPv6 into IPv4 packets)in its capacity as the Gateway between the LAN and WAN, and providing aplurality of IPv6 endpoints or devices that appear to be directlyconnected to the Gateway at the IPv6 level.

Physically, the endpoints or devices are capable of establishing radiotransmission paths to the Gateway directly (single hop to Gateway) or toother IPv6 devices (multi-hop to Gateway), and the algorithm and methodsof this invention describe how the network topology under the Gateway iscreated and packets are routed using the data link layer (Layer 2 in theOSI model). Devices or nodes power up, discover available networks,select the networks to join, choose an ordered set of viable upstreamcandidates as their next hop in their routing scheme, register with theupstream nodes having the best path and link cost, and ultimatelyregister with the Gateways associated with one or more of the availablenetworks. The network discovery process conducted by the nodes insuresthere are routes to forward packets upstream to the Gateway for egressto the Utility Host System, while explicit registration with theupstream nodes and Gateway provides the Gateway with the most currentnotion of the network and insures that traffic can also flow downstreamto the node. This is a multi-egress, multi-ingress routing scheme, wherea node can be part of multiple networks via one or more Gateways.

In a network that is typically represented by a utility network, thedistribution part of the network may include a plurality of nodeslocated at end-pint utility meters with a smaller number of nodes actingas relays, and one or more Gateways providing egress to these end-pointnodes. The utility network may also consist of the infrastructure part(substations, feeder stations, transformer locations, generationfacilities) that is populated with monitoring and control sensors. Thesedevices may also be part of the utility network that may be directlyconnected to the utility server via WAN or connected to the utilityserver via Gateways in the wireless network. The routing algorithm maybe structured in such a fashion that these infrastructure nodes, and anyselected distribution end-point nodes can establish bi-directionalconnectivity with minimal latency and via the fastest path. In someembodiments, these infrastructure nodes and select end-point nodes canhave multi-egress capability to increase network reliability.

The above and other features, including various novel details ofimplementation and combination of elements, will now be moreparticularly described with reference to the accompanying drawings andpointed out in the claims. It will be understood that the particularmethods and systems described herein are shown by way of illustrationonly and not as limitations. As will be understood by those skilled inthe art, the principles and features described herein may be employed invarious and numerous embodiments without departing from the scope of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates the overall network architecture of one possibleembodiment.

FIG. 1B is an alternate representation of the overall networkarchitecture of one possible embodiment.

FIG. 2 is a representation of the bit by bit structure of the link layerheader of a packet being routed.

FIG. 3 shows an exemplary format of the Network Advertisement messagesent out by a node about the best path to a particular network known byit.

FIG. 4 is a simplified representation of an exemplary routing tableconstructed at a node after it receives network advertisements from itsneighbors.

FIG. 5 is an example of a list of routes of different route types thatmay be present at a node.

FIG. 6 a shows an exemplary format for an “upstream registration”message sent by a node to another node upstream; FIG. 6 b is an exampleformat for an “upstream registration acknowledgement” message sent bythe upstream node to the registering node.

FIG. 7 a is an example format for a “Gateway registration” (AREG)message sent by a node to the Gateway it wishes to register with; FIG. 7b shows an exemplary format for an AREG message with neighborinformation; FIG. 7 c further illustrates the contents of an AREGacknowledgement message with network addresses.

FIG. 8 represents a sample network where multiple Gateways, relays andend-point devices come up one by one.

FIG. 9 shows an exemplary map of link costs between the nodes that canestablish RF communication links with each other in one possibleembodiment represented in FIG. 8.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, specificnomenclature is set forth to provide a thorough understanding of thevarious inventive concepts disclosed herein. However, it will beapparent to one skilled in the art that these specific details are notrequired in order to practice the various inventive concepts disclosedherein.

Some portions of the detailed descriptions that follow are presented interms of algorithms and symbolic representations of operations on databits within a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to effectively convey the substance of their work toothers skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of serial and parallel stepsleading to a desired result. The steps are those requiring manipulationsof physical quantities.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The subject matter presented herein also relates to an apparatus forperforming the operations herein. This apparatus may be specificallyconstructed for the required purposes, or it may comprise ageneral-purpose computer selectively activated or reconfigured by acomputer program stored in the computer. Such a computer program may bestored in a computer readable storage medium, such as, but is notlimited to, any type of disk including floppy disks, optical disks,CD-ROMs, and magnetic-optical disks, read-only memories (“ROMs”), randomaccess memories (“RAMs”), EPROMs, EEPROMs, magnetic or optical cards, orany type of media suitable for storing electronic instructions, and eachcoupled to a computer system bus.

The algorithms, processes, and methods presented herein are notinherently related or restricted to any particular computer or otherapparatus. Various general-purpose systems may be used with programs inaccordance with the teachings herein, or it may prove convenient toconstruct more specialized apparatus to perform the required methodsteps. The required structure for a variety of these systems will appearfrom the description below. In addition, the present invention is notdescribed with reference to any particular programming language. It willbe appreciated that a variety of programming languages may be used toimplement the teachings of the invention as described herein.

Wireless Network

Referring to FIG. 1A, a communications network may include a pluralityof devices 140 and 130 (“nodes”) linked to one another (at least one ormore) and to one or more Gateways within a wireless LAN 160. Unlessotherwise noted, Gateway may be alternatively referred to as “AccessPoint” or AP. The Gateway in turn may be linked to one or more backoffice utility servers (BOS) 150 via one or more networks 110, typicallyWide Area Networks (WANs). A back office server may be implemented onone or more computing devices, for example a utility server such as theserver 150 as shown in FIG. 1B, and may be implemented across one ormore networks.

Also shown in FIG. 1 a are infrastructure device nodes 170 IN-1, IN-2,and IN-3 located in wireless LANs 1, 2 & 3. There can be many moreinfrastructure device nodes (“IN nodes”) spread over the wirelessnetworks or the utility infrastructure. If these IN nodes are part ofthe wireless LANs, they may seek egress to the utility BOS via one ormore Gateways in the wireless LAN they are part of. In some embodiments,these IN nodes may have direct access to the utility BOS via a WAN orradio backhaul. In some embodiments, the IN nodes may also be linked toone another via radio.

Referring to FIG. 1B, nodes, such as battery powered devices (BPDs) 130and/or constant powered devices (CPDs) 140, and infrastructure devices160, may discover available networks 110 by listening to all neighborsit can set up links with, may select one they should join, and maychoose a set of viable upstream candidates as their next hop. Note thatin one embodiment, CPDs may act as a proxy for BPDs. However, alternateembodiments may allow BPDs to participate directly as nodes in thewireless network without a proxy. In certain other embodiments, the INnodes 160 may have direct access to the utility BOS via the WAN 110,instead of via the AP 120. In certain cases, many IN nodes are threadedtogether via radio add/drop backhaul system and linked to one anotherand the utility BOS.

EXAMPLE

Node M-1, a constant powered device 140 in FIG. 1A which is a node in awireless utility network 160, hears about access to Back Office Servers(BOS) 150 via one or more WAN network 110 (WAN-1 and WAN-2) from itsneighbors, and registers with both AP-1 and AP-2 of the type Gateway 120(with unique IP addresses) that provide egress to BOS 150 via one ormore WANs 110. It does this through the upstream nodes M-5, M-6, M-18,M-2 and M-12, of the type Constant Powered Device 140 in order tocommunicate with BOS-1 of the type utility server 150. Each of thesenodes may construct a routing table with an ordered list of next hopsand corresponding link costs (adjacency cost between the local node andthe next hop) and the path costs (advertised cost of egress by the nexthop). Each node subsequently registers itself with its upstream neighborand Gateway 120. Gateway 120 may keep track of the network topology andcapabilities of all devices in its control, and also other devices.Nodes may maintain local state and the states of their immediateneighbors, and may periodically update their registrations.

In one embodiment, the network nodes 130, 140 and 150 may be part of oneor more wireless LAN 160. In the example of a utility network, the LANmay be a neighborhood area network (NAN) corresponding to a neighborhoodor service area for the utility. As shown in the example embodiment,multiple LANs may be used, which may or may not overlap, such that agiven network device can be connected to (or be part of) only onewireless LAN or multiple wireless LANs. The nodes may be any type ofnetwork device. Examples of network devices, or nodes, include utilitynodes, which may include a utility meter or may connect to a utilitymeter. A utility meter is a device that is capable of measuring ametered quantity, typically a commodity like electricity, water, naturalgas, etc. Utility nodes that connect to a utility meter may include anetwork interface card (NIC) for communicating on a network, may includeone or more RF transceivers for communicating on one or more wirelessLANs, and may include one or more utility meter interface devices (agiven utility node may interface with multiple meters, which may or maynot meter different commodities, such as electricity, gas, water, etc.).Utility nodes may also include an in-premise device interface to connectto in-premise devices through an in-premise network (which may or maynot be a wireless network). In-premise device interface connects toin-premise devices to provide a communications link between the utilitynode and the in-premise devices. Additionally, the utility node mayprovide a communications link between the in premise devices and thewireless communications network connected to the utility node. Otherexamples of network devices include communication devices, such asset-top boxes (as may be used in cable television or satellitetelevision delivery), household appliances (e.g., refrigerator, heater,light(s), cooking appliances, etc.), computers or computing devices(e.g., game consoles, storage devices, PCs, servers, etc.) networkingdevices such as relay, Gateway, router, phones or cell phones, batterystorage device, transportation devices, transportation vehicles (forexample: an electric or hybrid car or other vehicle, which may or maynot be able to “plug-in” to a utility grid to receive ametered/monitored commodity such as electricity), entertainment devices(e.g., TVs, DVD players, set top boxes, gaming consoles, etc.), or otherdevise which may be found in a home, business, roadway or parking lot,or other location. Relays 130 (one example is M3 in FIG. 1 a) may handlecommunication between network nodes 140 and the Gateway 120. Forexample, a relay could provide communication between the network nodeand the infrastructure of the utility network. Unless otherwise noted,other devices in the network such as meters, electronic devices,Gateways, etc. may also perform as relays, and relays may perform thefunctions of other devices or software on the network. The wireless LAN160 may be any type of wireless network, and may use any frequency,communications channel or communications protocol. In some embodimentsof this invention, one or more of the wireless LANs 160 are FHSS(Frequency-Hopping Spread Spectrum) networks or DSSS (Direct SequenceSpread Spectrum) networks.

The wireless network 160 may be connected to one or more gateways 120. Agiven wireless network may be connected to only a single gateway, or maybe connected to two or more gateways. The gateways 120 may be connectedto one or more wide area networks (WAN) 110. The WANs 110 may beconnected to one or more utility back office servers (BOS) 150. The backoffice servers may handle a variety of business or management tasks,including participation in the collection of metering information,managing metering devices, security for the network, or other functionsas may be desired in an AMI network. Examples of back office systemsinclude billing and accounting systems, proxy servers, outage detectionsystems (as may be used in a utility network), data storage systems,etc.

In one embodiment, the routing protocol used is a “next-hop”multi-egress/multi-ingress algorithm for determining an optimal routeto/from a destination, which may use path cost and/or history of stableupstream and or downstream routing as the metric for determining thenext hop for routing packets. In one embodiment, hop counts are not usedfor evaluating the path cost, but are used to prevent routing loops, asdescribed below. In such an embodiment, a node may select the route withthe lowest metric value of the path cost in selecting the preferredroute to transmit packets.

In one embodiment, in the initial network discovery phase, a node mayuse a process to scan through slots or channels to get to its neighborsand to get acknowledgement responses and an initial value of linkquality estimates from those discovered neighbors. This initial linkquality estimate may be used to select a number of best upstreamneighbors to talk to (the number selected may be configurable).

A node proceeds with the “Registration” process with its upstream nodes,when the node intends to use these upstream nodes for egress to anothernetwork. In response to the registration message from the node, theupstream node will add the registering downstream node to the downstreamrouting table entries maintained by the upstream node. The upstreamnodes may also proceed to maintain up-to-date timing information aboutthe registering node in response to the registering by the downstreamnode. Nodes routing through each other are preferably set up to exchangetiming information periodically in order to remain in sync and exchangepackets in the wireless network. In one embodiment, the wireless networkmay be based on frequency-hopping spread spectrum (FHSS). In anotherembodiment, the timing updates piggyback on any data transfer messages,but an explicit timing information exchange may be triggered if therehas been no data exchange for a preconfigured interval (for example, onthe order of 30 minutes).

The registration of a node with one or more of the Gateways may thentake place. This registration process can prompt the Gateway to add theregistering node to its routing table and insure that the status of thenode is up to date. The registration of a node with the Gateway mayoccur periodically but more infrequently than the registration with anupstream node. In the presently preferred embodiment, the frequency ison the order of once every 12 hours.

Addressing

IPV6 Addressing:

Each node 130, 140 in the wireless communication network may beidentified for end-to-end routing in any particular network by a uniqueIPv6 address. IPv6 addresses are typically composed of two logicalparts: a 64-bit network prefix and a 64-bit host part. Upon successfulregistration by a node with the Gateway, the Gateway may hand the nodedata packets in the form of a TLV (Type Length Value) containing thenetwork configuration, including the IPv6 globally routable prefixassociated with the subnet the node is joining. The node may then send aDynamic DNS update request (RFC 2136) to the Network Host Utility System(BOS) DNS server. When a utility server (BOS) 150 wishes to send trafficinto the Wireless LAN, it may resolve the node's DNS name into an IPv6address for Layer 3 (IP) routing through the WAN to the correct Gateway.If the WAN is IPv4-based, IPv6 packets may be encapsulated within IPv4with appropriate prefixes for tunneling through the IPv4 cloud. At theBOS 150 and the gateway 120, the received IPv6 packet would bedecapsulated.

A node may register with multiple networks either on the same Gateway oron multiple Gateways, in which case, it may set the priority order forthe networks it belongs to based on its estimation or calculation of thelowest cost path. In the presently preferred embodiment, the node willhave an IP address for each network it is registered with. The DNSserver may associate these IP addresses with the node's hostname in apreferred order according to the policies defined on the DNS server.When a BOS Server in the WAN network wishes to send traffic into thewireless LAN, the DNS server goes through the candidate IPv6 addressesin order while resolving the node's hostname.

Link Layer Addressing

Each node 130, 140 may be identified for routing in the Wireless LAN bya unique link layer address assigned to its radio interface. In thisembodiment, each node may have only a single interface. Otherembodiments can have multiple discrete link layer addresses. Link layeraddress is typically 8 bytes long and is the device's MAC address. Thelink layer broadcast address may be hex ff:ff:ff:ff:ff:ff (all ones).Packets transmitted with this local broadcast address can be processedby those who receive them.

RF Link Layer Packet Forwarding

FIG. 2 illustrates the bit composition of the link layer header that maycarry the information as explained in Table 1 below. Also described inthe Table are the flags carried by the link layer header.

TABLE 1 Bit(s) Name Description  0-3 Version Protocol version number. Ifa higher version is received, the frame is discarded.  4-7 Protocol IdHigher layer protocol id: 0x03: SSN routing protocol 0x04: IPv4Networking protocol 0x06: IPv6 Networking protocol 0x07: Datalink trace 8-12 Address Count Indicates the total number of addresses contained inthe data link header, including the source, destination and anyintermediate addresses for source routed packets 13-17 TTL This is setwhen the packet is generated. The initial value is set to ‘Default TTL’and is configurable. The TTL is decremented every hop that the packettraverses. 18-22 Current Offset Set to 0 on packets that don't usesource routes. This is set to 0 when the packet is first sent into thenetwork. It is incremented at every hop the packet traverses. 23-25Priority The DLC layer supports 8 levels of priority, this field mapsdirectly to those priorities. 26 Source Route Bit Indicates whether thepacket contains the entire hop-by-hop route to be used between sourceand destination. 27 Preserve Source Set when the L2 forwarding codeshould Route preserve elements in the source route when forwarding apacket downstream. If this is not set, the L2 forwarding code may stripout intermediate hop addresses once it has made a forwarding decision.28-31 Reserved Reserved for future use

As illustrated in FIG. 2, the flags are followed by the source addressof the node generating the packet. In one embodiment, the source addressof the flag may not be set to the broadcast address.

As illustrated in FIG. 2, the source address may be followed by theaddress of the next hop the packet is to be sent to. In one embodiment,if the Source Route bit is set then the entire list of hop addressesending in the destination address can be included, otherwise only theone next hop can be specified. In either case, the final address is thedestination the packet is to be routed to.

If the source route bit is set, the packet header can contain the fullpath the packet will take. Note that a packet can be source routedbetween two nodes with no intermediate hops (i.e., Add Count is 2, andthe destination address is either a node or broadcast address). This isa mechanism that may be used to interrogate individual nodes 130, 140from a terminal such as a debugging mobile station.

If the source route bit is not set, the L2 forwarding code on a node maymake a decision based on the value of the Address Count field. Forexample, if the Address Count is equal to 1 on a packet being sent fromthe RF LAN towards WAN network (110) or utility Server (150), it meansthe packet can be forwarded to any egress node or Gateway in the system.If the Address Count is greater than 1, it means that all additionaladdresses in the forwarding table at the node are allowable L2 egressdestinations. The addresses in the forwarding table for a network can beordered by preference, from least desirable to most desirable.

If the Address Count is greater than 1, the packet can be rerouted to adifferent L2 destination in case of congestion or failure. When adifferent L2 destination is chosen, the previous network should beremoved (either by decrementing Current Offset or zeroing out theprevious field). Removing the previous network is intended to helpreduce the occurrence of routing loops, where a packet could bere-injected further away from the destination than the original source.

The TTL may get decremented when a packet goes through a node's L2forwarding. Packets going through L2 forwarding can be dropped when theTTL becomes zero; messages with a zero TTL destined to the local hostcan be delivered up the stack. Nodes 130, 140 that are sending messagesto the Gateway 120 without using full source route may set TTL to be atleast the number of hops on the longest path they have leading to theGateway 120. The maximum TTL may be configured by the administrator. Inone embodiment, packets sent with the destination address set to L2broadcast are not forwarded.

Delivery of unicast packets can be acknowledged by the DLC (Data LinkControl) layer. Broadcast packets may be implemented as unicast packetsin the FHSS scheme, and can also be acknowledged. It may not be possibleto send unacknowledged unicast packets. When a node 130, 140 sendspackets to a neighbor, the MAC layer may report the number of retriesand the eventual success of the transmission. The network layer may keepcounters of this information on a per-neighbor basis.

Routing Subsystem

In one embodiment, the routing subsystem may be divided into fourfunctional components:

neighbor scan and discovery

neighbor maintenance

node registration with upstream neighbors

node registration with the Gateway

One embodiment of the routing subsystem can utilize the code entity DLF(Data Link Forwarder) for Layer 2 routing and the code entity MLME(Media Access Control Sub-Layer Management Entity) for acquiringneighbor nodes and maintaining timing information between neighbors. TheDLF interfaces to the MLME through a set of APIs.

Neighbor Scan and Discovery

Nodes such as CPD 140 (FIG. 1 b) may initiate network discovery when,for example:

-   -   It has no viable egress nodes (it is not associated with any        Gateways)    -   Communications with upstream nodes have been severed, either        administratively, or due to part failure or propagation loss    -   A periodic registration message to one of its Gateways has        failed at least 3 times    -   A new network is advertised

Nodes such as BPD 130 may initiate network discovery, for example, ifthe link to its nominated master (CPD node 140) has been severed.

In the example embodiments, a node may discover neighboring nodes usingtwo basic processes: broadcast discovery and neighbor queries. When anode comes up, the MLME may find all of the node's adjacencies (ordirectly connected RF links) through a “broadcast discovery process”. Itmay do this randomly to determine when it should start sending broadcastdiscovery frames and then choosing the channel on which to send thebroadcast discovery frame (channel selection may be done randomly). Itmay then cycle through every slot, transmitting each successivebroadcast discovery frame on the next slot, wrapping at the last slot.In one embodiment, this process can guarantee that a broadcast discoveryframe is sent on every channel in the hopping sequence of the FHSS-basednetwork.

In the exemplary embodiments, there can be two modes to broadcastdiscovery: aggressive and passive. When powered on, the device node mayenter aggressive discovery mode where it sends out discovery frames atrandomized intervals that may be in the order of milliseconds. It mayenter passive discovery mode when the aggressive discovery duration hasexpired. In passive discovery mode, a node may wait a much longer timebetween sending broadcast discovery frames, typically of the order ofminutes.

Once the discovery process has found a neighbor (adjacency), or a set ofneighbors, the MLME may then query the discovered neighbors for theirdirect neighbors (the direct neighbors can be provided in response).This may be done to discover the network environment more quickly (incontrast to broadcasting a large number of frames in hopes of contactingany one particular device). The neighbor query mechanism can be a simplequery/response: a node receiving a neighbor query applies the criteriato the nodes in its list and, the nodes that “match” the criteria areplaced in the neighbor response. If no criterion is given, all the nodesin the list may be placed in the neighbor response.

The MLME may notify the DLF when discovery is over i.e. the nodes havebeen queried for their neighbors and an attempt has been made to reachthose neighbors.

Using the list of neighbors built up by the MLME, the DLF may try andfind advertised egress routes. It may accomplish this task by listeningfor “Network Advertisement” (NADV) messages from the nodes in the MLME'sneighbor table.

The NADV message may advertise a set of egress routes, which may includethe path cost and hop count of the egress routes. Path cost can be thelowest cost associated with that egress (Gateway), amongst all candidatepaths. Hop count can be the highest number of hops that are taken toreach that egress. Hop count can be used to prevent routing loops, andmay not be used in conjunction with the path cost. An example of theformat of the NADV message is shown in FIG. 3. The Destination MACaddress can be the MAC address of the node originating the networkadvertisement. In most cases it can be the egress point (or the Gateway)since networks can be identified by their egress nodes.

From the advertisements received in the form of NADV messages, each nodecan construct a routing table listing the networks available, the egressnode (Gateway) identifying each of the networks, and the available pathsto that egress node. Each of the available paths can be described with anext hop, flags describing the type of path, and the link and pathcosts. The flags can indicate the kind of route—whether it is apermanent entry in the table, whether it can be advertised by the nodeetc. In one embodiment, the node can decide to register with thatupstream node for which the total cost (link and path costs) to thenetwork is the least. Other embodiments may use other criteria includingvalidated reliability of the link in providing long-term egress to thenetwork. An example of the information that may be captured in therouting table is laid out in FIG. 4.

From the routing table information, nodes may construct a forwarding ornext-hop table with a list of destination MAC addresses, a typeassociated with each address, and the path cost for it. In oneembodiment, the type reflects the selection preference associated withthe destination and may be one of the five: source-routed, hop-by-hop,direct adjacency, breadcrumb, or local. FIG. 5 provides an example ofthe route types that may be listed. In one embodiment case of adestination of the hop-by-hop type, it can be listed along with the nexthop from the source node. In the case of a destination of thesource-routed type, an array of hops can be explicitly stated with thedestination in the forwarding table. Multiple entries for the samedestination may be listed in the order of preference, which may bedetermined both by the type flag and the path cost. In one embodiment,when trying to reach Destination 4, the node can first use one of thehop-by-hop entries that are maintained in a linked list in order ofincreasing path cost. In other embodiments, the routing algorithm allowsfor the routing information maintained at the source node to create asource route entry for Destination 4, by structuring a forward set ofpaths to the destination address. Yet, in other embodiments, the nodecan use the breadcrumb route it had picked up from passing traffic atsome point in time.

Neighbor Maintenance

In one embodiment, upstream and downstream neighbors can be constantlymaintained via MLME beacons or targeted periodic keep alive messagesused for synchronizing the clocks and assuring that nodes can stillexchange packets with each other. This constant contact and feedback maybe used by the L2 routing layer for multiple purposes, which mayinclude:

-   -   Neighbor updates are communicated to downstream devices in        timing update beacons.    -   Nodes use the MLME to detect if their downstream or upstream        node is still functioning.

A node's upstream link characteristics may change, for example, when:

Upstream node is no longer available

A new preferred upstream node is detected

Link quality changes (smoothed over time) have taken place

In one embodiment, these rules can be applied recursively, to allupstream nodes in a path. When an adjustment occurs, the noderecalculates the costs to each of its egress nodes. When a node's costto its upstream node significantly changes the cost to one of thenetworks it routes through, it can distribute this information in thenext set of MLME beacons to its downstream nodes.

In one embodiment, a change in network information can be propagatedwith a “Neighbor List” message, with the protocol type field set to 0x2indicating that a partial list of changes is being distributed. In oneembodiment, this can reflect adding new networks or changing the cost ofexisting networks. When an upstream node disappears, causing aparticular network effectively become no longer routable, a “NeighborList” message can be sent with the protocol type set to 0x3 to indicatethat the network has been removed from the upstream nodes network list.

In one embodiment, each Gateway is notified about changes in networktopology by the periodic network registration messages that are unicastto it. These messages may be sent by every node within the Gateway'snetwork, and may contain a complete list of their upstream nodes, andthe link costs to each of them.

In one embodiment, the MLME keeps two smoothed averages that can be usedby the DLF for determining link costs for routing purposes: a smoothedRSSI and a smoothed info success percentage. The term “smoothed” refersto the type of averaging done on the data. In one embodiment, theaveraging uses the formula: smoothed average=A*average+B*sample;B=(1−A). This type of averaging does not require a large amount ofmemory for storage (as opposed to storing the last N samples) and alsohas a controllable amount of “history”. The term history refers to howmuch the new value affects the current smoothed average. This may becontrolled by the A and B values: large A values mean that the averagehas more history than smaller A values. Other embodiments can use otheraveraging techniques that are desirable under the prevalent networkconditions.

The RSSI is the received signal strength indicator. This value may bemeasured for all frames received from a node. In some embodiments, itonly has limited use in link quality calculations as it may not give aclear indication of the bit error rate of the link. When any frame isreceived from a node, the RSSI of that frame can be averaged into thesmoothed RSSI using the averaging formula.

In one embodiment, the “info” success percentage criterion can be usedas the best measure of link quality and therefore in making routingdecisions. The “info” success percentage is a form of packet successrate. The term “info” is used to denote frames other than the ones thatstarted the communications. The first frame sent to a node targeted onits hopping sequence can fail due to interference or due to the receiverbeing busy. The info success percentage, in including only those framesthat the targeted node is listening for and not the frames at the startof the communications, provides a link quality measure that may not varygreatly with the load of the receiver. The info success percentage maybe a better indicator of link quality.

Node Registration with Upstream Neighbors

Each node may explicitly register with the upstream nodes it intends touse in a network. This registration means that the upstream node may nowattempt to keep up-to-date timing information about the registeringnode, and keep a downstream routing table entry. Thus, traffic cannotonly flow towards the egress, but also back to the node (downstream).

The node registers with its upstream node by sending it an “UpstreamRegister” message. The “Upstream Register” message may contain thedevice's type, and a neighborhood health metric. The neighborhood healthmetric can be used to cull downstream nodes when an upstream becomesoverloaded. Devices with a low neighborhood health metric (and thereforepresumably low path diversity) can be preferentially selected beforedevices with high neighborhood health metrics.

An exemplary format for the “Upstream Registration” message is specifiedin FIG. 6 a. The message type indicates it is an upstream registration.The neighborhood cost is the neighborhood health metric based upon acombination of the numbers of potential and active upstream nodes.

Potential upstream nodes either positively or negatively acknowledge“Upstream Register” message using an “Upstream RegistrationAcknowledgement” message. A device's “Neighborhood Health” can beupdated based on the value of this acknowledgement. Potential upstreamnodes can give less weight than acknowledged upstream nodes.

An exemplary format for the “Upstream Registration Acknowledgement”message is given in FIG. 6 b. The type indicates that it is an “UpstreamRegistration Acknowledgement” message. The “Seq Num” is the sequencenumber sent by the requester in the “Upstream Registration” message. Thestatus code of the response can be one of the following:

0x0, Node successfully added

0x1, Node failed to be added

0x2, Node rejected due to high load

0x3, Node is already being maintained

Node Registration with AP

A node can register itself with a Gateway by sending a unicast “APRegister” message (AREG). The AREG message can contain the list ofaddresses of nodes in the Gateway's network that the registering nodeuses as upstream nodes, and the link cost associated with each of theseupstream nodes. It may also contain a list of other candidate networks(represented by the egress nodes of those networks), and their cost.

An exemplary format of the AREG message is given in FIG. 7 a. The Typecan be set to indicate it is an AREG message. The M bit can be set ifthere is more data to send. Seq Number can be the sequence number of theregistration message. Message number can be used when the registrationmessage is sent in multiple parts. Each AREG Neighbor can describe anupstream node in the paths used by the registering node.

An exemplary format for an AREG Neighbor description within the AREGmessage is given in FIG. 7 b. The MAC address can correspond to theupstream node or a network egress point that the registering node isinforming the Gateway about. Cost can be the recorded cost to either theupstream node or the network egress point being described. The E bit isthe Network Egress Node bit. It may be set if the neighbor descriptionrepresents a network egress node and not an upstream neighbor.

In one embodiment, when the node is successfully registered with theGateway, the Gateway can place the node in its routing table, and keepsan up to date state on the node. The node can send periodic registrationmessages to the Gateway (on the order of every 12 hours.) The Gatewaymay update its routing table when it sees subsequent Gateway (AP)registration messages. If the Gateway misses three consecutiveregistration messages, the node may be culled from the Gateway's routingtable, and the node may need to re-register itself.

In response to a successful first time registration, the Gateway cansend down a set of TLVs containing any network configurationinformation. This list may include, among other things, the Gateway'sglobally routable IPv6 prefix, Gateway's MAC address, DNS serveraddress, network transmission timers and any other variables relating toL2/L3 routing. FIG. 7 c is an example gateway AREG message to theregistering node with network addresses.

If a Gateway becomes overloaded with too many nodes it can begin to cullnodes that have other candidate networks. It may evaluate this bylooking at the different networks reported in the AREG messages, and mayremove the healthiest candidates from the network, and notify them ofany such action taken.

EXAMPLE

A small-scale RF network depicted in FIG. 8 may be used to illustratethe preferred embodiment of how the route determination and propagationworks in a typical scenario where the Gateways (821, 822, . . . ) andrelays (831, 832, . . . ) are brought up first and then end-point nodes(841, 842, 843, . . . ) are brought up. As illustrated in FIG. 9, thelink costs are mapped between nodes that establish communications witheach other in the RF layer.

In the example illustrated in FIGS. 8 and 9, nodes M1, M2 and M3 eachestablish routing options to Gateways AP1 and AP2 for egress based onadvertised path costs they receive from their neighbors including R1 andR2. In most cases, each node will have multiple, prioritized routingoptions via one or more of their neighbors in the next-hop (NH)configuration.

In one embodiment the routing mechanism can be adapted to be compatiblewith, and take advantage of, the Frequency-Hopping Spread Spectrum(FHSS) access scheme used in the wireless network of one embodiment, andleverage some of the inherent operational features of FHSS. Regulartiming updates occur in the frequency hopping technique to address clockdrifts at various nodes that should remain in synch to synchronouslyexchange packets. The routing protocol can keep packet overhead to aminimum by using the frequency hopping timing updates as “keep-alive”messages for sending link status information. Alternately, timingupdates can also piggyback on any data packets that are forwarded.Unless otherwise noted, keep alive messages can be messages sent toupdate information, and may be sent regularly. “I'm alive” messages,which may also be used to update routing information, can be typicallysent to announce, for example, when a node is initially powered on orintroduced into a network.

In such an embodiment there can be no broadcast in the conventionalsense in the routing protocol on a network utilizing FHSS scheme. Nodescan be targeted directly one by one for packet exchange. The routingprotocol presented herein can use an abstraction of a broadcast wherebythe link layer broadcast frame using the 8-byte MAC address of all ones(ff:ff:ff:ff:ff:ff in hex) is transmitted on every slot or channelstarting at a randomly chosen slot and with a predetermined wait timebetween each transmission.

In one embodiment, the routing protocol described herein uses beaconingcapability in an FHSS-based wireless network where a beacon is aperiodic broadcast on a certain known frequency hopping sequence thatall neighbors can recognize. The broadcast beacon that can be receivedby multiple neighbors can be more efficient than sending a routingupdate to each neighbor. A beacon can also be a shorter transmissionwith lower overhead than a routing update as there can be noacknowledgement messages and therefore less re-transmission packets uponfailure.

In one embodiment the routing protocol described herein is designed toexploit the collective computing resources of the devices (nodes) in thenetwork instead of relying on one Gateway at the root of the wirelessnetwork to calculate and distribute routes to all nodes. The end-pointcan select a preferred set of an ordered multiplicity of upstream nodesto use as next hops to go out to a WAN network through multiple Gateways(also referred to as APs) based upon the egress route advertisementswith the associated path costs for each route and each hop. Upon failureof the primary route upstream or to the Gateway, the fall back tosecondary routes and/or Gateways in the end-point's database can beimmediate without any wait for a routing algorithm to re-converge sincethe routes are already pre-converged.

In one embodiment, the routing protocol allows nodes to migrate from onenetwork to another network. When an upstream node advertises its knownroutes to a downstream node, it can send out a set of egress routes toavailable networks. The routing table at each node lists next hopsthrough multiple Gateways for available networks, making a quickmigration possible in case of the primary or default network becomingunavailable.

In one embodiment, each node registers itself with the upstream nodes itintends to use. The upstream node can now keep a downstream routingtable entry for that node. Traffic destined for an end-point can now berouted primarily hop by hop where the next hop from the source or anynode subsequently can be added to the message header of the packet. Ofcourse, the destination address can be routinely included. Sourcerouting where the ordered list of nodes through which the packet passescan be explicitly stated by the Gateway in the message header is alsowithin the scope of this algorithm as a secondary option. The routingprotocol disclosed herein can allow each node to have multiple next hopsin its knowledge base and gives it the ability to choose from them forhop-by-hop forwarding. By doing so, the packets can circumventproblematic links without transmission failures and retransmissions, andcan be more advantageous in a wireless network where the RF links tendto be transient in nature. In addition, this can avoid open-ended routediscovery loops and problem route issues that source routing techniquesare forced into in the presence of failed links.

As an integral part of the routing implementation in a utility network,there can be many functionalities that are implemented to assure thatthe network and the nodes are operating optimally. The disclosure hereindescribes several innovations that enhance the network performance,utilizing the same routing functionalities as described earlier.

Configuration Management

Nodes in the network may have the appropriate and latest configurationon them, and distribute this configuration information to other nodes inthe network. For the utility back office server (BOS) to manage thenetwork, the network nodes will need to have end-to-end reachability.The nodes can be properly configured and provided with adequateinformation about the overall network configuration, by utilizingupstream nodes as proxies for distributing configuration information.

There can be certain “settings” on network devices (nodes) that arefield/site specific. These settings can be represented as configurationvariables on the device. A configuration variable can be written topermanent storage once it has been set. Examples of these settings are:the DNS server that meters use, SNTP trap host, time zone information,etc.

Further, some configuration variables can also be “knobs” that can beused to tune how the network performs, e.g., the rate of sending networkregistrations, some smoothing parameters that may be used in thelink-cost algorithm. There may be instances when the knob is tuned on anetwork-wide level to change the behavior of multiple devices in thenetwork. To achieve these capabilities, it may be useful to distribute,implement and manage the configuration levels at the device and networklevel at all times.

The disclosure presented herein provides a method for executingconfiguration management. When nodes send a routing registration to theGateway (NREG), they may include a SHA-1 hash (secure hash algorithm) oftheir configuration. If the SHA-1 hash does not match the hash stored onthe Gateway, then the Gateway can send the node its new configuration.This SHA-1 hash may contain:

The list, or identification, of variables to be included in SHA-1

The variables to be used in the SHA

The list of variable can be important, because if there is a need toinclude new variables in the configuration SHA-1, changing that listwill cause a SHA-1 mismatch.

Time Synchronization:

This item is related to Configuration Management, but the uniqueness isin the concept of embedding time synchronization into networkregistration (NREG) messages. Instead of making separate requests to aback office time server, or a time server on the Gateway, when a devicesends a NREG message, a new node or a rebooting node can be given timeas a part of joining (re-joining) the network. This innovation bringsseveral advantages including: (a) it can make timing informationavailable almost immediately (b) can save at least two end-to-endpackets.

The time-sync distribution may typically have a basic request/responsemechanism in a network. Network nodes can be configured to request timefrom a specific MAC address. If that address is not configured in thenodes, they can ask for time from a Gateway in their routing table.Gateways can run SNTP (Simple Network Time Protocol). If the Gatewayshave time, they can respond in the following way: the response packetcan be time-stamped by the application layer. When the packet is handeddown, it can be “marked up” with a transmit delay at the MAC layer. Thepacket can have a field for total transmission delay, and this value canbe updated at each hop. When the requesting node receives the response,it can add the time-stamp value and the transmission delay to get thecurrent time. For efficiency there can be a “flag” in the packet thatindicates it should be examined at each hop. This can be ageneral-purpose flag and may be reused for other protocols (for example:traceroute).

The timesync request may be sent as a standalone IP packet (for example:IPv4 or IPv6), or it may be combined in a network registration (NREG)packet for efficiency. It is not directly included in the networkregistration packet's payload, rather it is inserted in a data-linkinterface (DLI) TLV. The DLI TLV can be processed before the packet ishanded up to the application. If the Gateway receives a time-syncrequest with a network registration, the reply can be included as a DLITLV in the network registration acknowledgement (NREG ACK).

Local Load Management by Network Nodes

It can be desirable to avoid a situation where the nodes in the network“line up” behind the best-cost node and use it for routing. The node mayquickly become too busy to forward traffic for all nodes that are usingit. This can also make the routing fragile causing congestion and maymake many nodes to become unreachable. Further, there can be a lot offlap to form new routes.

The innovation disclosed herein can force the preferred nodes toincrease the cost advertised to a random set of neighbors. The preferrednode(s) may receive(s) “keep” packets from nodes that are using it. The“keep” packet may be a request from the downstream node asking theupstream node to continue to include the node in its active packetforwarding (routing) list. If the preferred node has too many activekeep nodes, it can increase its path-cost (according to an algorithmdesigned to achieve a specified but variable percentage decrease inpacket traffic) and may send this new cost to a random selection ofneighbors that it wants to drop or to a number of neighbor nodesselected according to a load balancing or traffic balancing algorithm.It may continue to send actual cost to the rest. A goal of this exerciseis to discourage a smaller (but predetermined percentage) set of nodesto leave the preferred node. The algorithm can take into account twofactors to avoid huge swings in network traffic:

forcing large number of nodes seeking alternate routes and creatingrouting loops, by distributing “high” path costs to a large percentageof nodes.

avoiding situations when downstream nodes continuing to receive actualpath cost do not inadvertently advertise this cost to those nodes whohave received increased path costs from the preferred node, forcing themunder some circumstances to route the packets through the advertisingnodes back to the preferred node.

Keep packets can be sent at regular intervals and may not vary likenetwork traffic. They can be sent at roughly the same rate as the routeadvertisement period, so the nodes should have the keep feedback by thenext advertisement period. In one embodiment, the rta (routingadvertisement) period can be set at 20 min and the keep period can beset at 10 min.

It may be assumed that nodes do not switch to better or alternate routesunless their cost to the current upstream neighbor for egress increasesby 10%. Therefore, in one embodiment, the algorithm used can force theupstream node to increase the cost of the route by ˜10%. In oneembodiment, the route cost increase is kept to less than 20%. Otherwise,it may trigger an rta if the nodes begin to switch and cause moretraffic down stream.

The downstream nodes may also be selected randomly over all the nodesthat the preferred upstream node is sending the rta to, not just to thenodes that are sending it the keep messages. This may discourage onesthat will immediately switch to the preferred node if their routingsituation forces them to opt to the preferred node. This is an effectivepreventive solution to avoid receiving a flood of registration requestsfrom new downstream nodes.

Local Load Management by the Gateway

In some network situations, some Gateways can get overloaded withtraffic in the field while other Gateways have very few nodes registeredwith them, thus causing a traffic imbalance. One exemplary method ofmanaging traffic flowing into a Gateway may be to control the number ofnetwork nodes that register with the Gateway. On the other hand, theGateway may control the registrations in such a way as to prevent nodesfrom getting stranded (i.e., they are unable to register with anyGateway).

In the routing algorithm disclosed herein, there can be at least threemechanisms for controlling the number of network nodes that registerwith a Gateway:

-   1) The number of hops a routing advertisement propagates out into    the network-   2) Gateway pushback (sending negative NREG ACKs)-   3) Raising the routing cost that the Gateway advertises (in cases    where the Gateway advertises routes in behalf of several selected    nodes for providing egress to the registering nodes)    Hop-Count Control:

The routing algorithm disclosed herein has the ability to tune thenumber of hops that routing advertisements can be forwarded out into thenetwork. The algorithm may also include a basic feedback controlalgorithm. One type of such algorithm may be Gateway-specific, where theGateways adjust their hop count individually based on a target number ofnodes that the Gateway wants to have in its registry. The second typemay be a control loop that may be global where Gateways adjust their hopcounts relative to each other. If one Gateway has more registered nodesthan another, it can lower its hop count while the other one raises itshop count.

Gateway Pushback:

In one embodiment, the nodes can tell the Gateway if it is theirprimary, secondary or tertiary route when they register with theGateway. The Gateway may have hard limits for the number of routes atwhich it starts sending negative acknowledgements (NACK) to tertiary andsecondary nodes. In one embodiment, the Gateway may not send NACKs toprimary NREGs in order not to let the nodes stranding.

Once the number of routes (nodes) that a Gateway has registered is abovethe limit set for managing the network traffic, the Gateway may startsending NACKs to any node trying to register as a tertiary route. Thesecondary NACK level may be higher than the tertiary NACK level. Whenthis level is reached, the Gateway may start sending NACKs to bothtertiary and secondary registrations.

When a node receives an NACK from a Gateway, it may place it in ahold-down list. Advertisements from a Gateway that are in the hold-downlist may be thrown away. Placing the Gateway in the hold-down list mayprevent the node from registering with it again immediately. A node mayre-initiate registration with a Gateway after it receives a message todo so along with a route advertisement message from the Gateway. Oncethe Gateway is removed from the hold-down list, the node may re-registerwith the Gateway. In one embodiment, a Gateway can be placed on thehold-down list for 3 hours after an NACK. If a node loses all routes formore than a certain period, it may be assumed the network has changedsignificantly. In this case, Gateways that the node received NACKs frommay be taken off the hold-down list.

In yet another embodiment, another variation of Gateway push-back may beused by having the Gateways synchronize globally with each other to setthe secondary and primary levels. The level may be varied depending onhow loaded the other Gateways are in comparison.

Route Evaluation (Discovery and Maintenance)

Link Evaluation

When a node is discovered, the MLME (MAC Layer Management Entity) of thesource node may have no idea how good a neighbor the discovered node is.As such, it may want to evaluate its routing success to that node. Inone embodiment, the evaluation phase includes sending a node 20 packets(configurable) and then calculating how many of them succeed (in thisembodiment, an exponential filter can be used for evaluating the linkinfo success). The source can send its latest link cost in theevaluation packet. Each evaluation packet can also be acknowledged. Thisprovides that 1) the neighbor is able to talk back to the node, 2) thesource node knows what the neighbor's link cost is to it. Knowingbi-directional link costs can be important for routing, because thetraffic travels back downstream. The bi-directional link cost can alsobe included in the keep packet acknowledgement that the source nodesends to the upstream nodes it may use for routing later.

The evaluation process may result in considerable packet traffic. A nodemay not be able to evaluate its neighbors all at once. However, thesource node can evaluate the best nodes first so that the node may startparticipating in routing. Therefore, in one embodiment, the source nodeselects a configurable number of best RSSI neighbors, and evaluates themfirst. In one embodiment, the number is set at five (5).

Keep Mechanism

In a wireless ad hoc network, nodes may keep some information abouttheir neighbors. This information can be stored in a list. As presentedherein, the list is referred to as “nodeq”.

The keep mechanism may have three purposes:

1) Let neighbor nodes know that they are upstream for routing and thusthey should not drop the node sending them keep messages from the nodequnless there is a real need;

2) Obtain bi-directional link info so that route path cost can beestimated;

3) in case a node was dropped from an upstream's nodeq they will knowabout this as soon as possible (in one embodiment before the 2×20 minuterouting advertisement period has passed).

The keep mechanism can work as follows: the MLME of the source node cansend keep packets every 10 minutes to the upstream nodes that therouting layer is using. The keep packets can be acknowledged, and theacknowledgement may contain the link cost from the upstream to the node.

1) When a node receives a keep message, it can mark the transmittingnode as a keeping node, and may not cull that node from the NODEQ.

2) Keep messages may give the node a way of knowing what the upstreamlink cost is. In some embodiments, if keep messages are not transmitted,there may only be very infrequent traffic from a downstream node to anupstream node. One example may be when a utility meter is read only oncea day. In this case, the keep message traffic may be useful to keeproutes stable in a network with very infrequent, bursty traffic. In thedownstream direction there may be traffic every 20 minutes in the formof a routing advertisement. Sending periodic keep packets thusfacilitates measuring of the link cost and communicating it to bothnodes so that they may keep updates of bidirectional link cost.3) When a node is dropped from an upstream's nodeq, the dropped node mayreceive a “cull” message from the upstream node immediately. However, iffor some reason the dropped node does not receive that message (forexample: when a node has just rebooted, etc.), it may infer that it wasdropped if it does not receive the keep acknowledgement during its nextkeep message cycle. And this can happen faster than the exemplary timeof about 40 minutes allotted for expiry of routing advertisements. Thus,it can make the network more reactive to changes and it can adaptfaster.Link-Evaluation Algorithma) Direct Link Evaluation Via Info Success Percentage:

In one embodiment, the Data Link Layer (DLL) of the nodes communicateswith neighbors by first polling them to see if the neighbor isavailable. If the poll acknowledgement is received, the data frame canbe sent. This exchange is called a PADA exchange (POLL-ACK-DATA-ACK).When no acknowledgement (ACK) is received to the poll or data frame, arandom back-off time can be generated, and re-transmission can occurwhen the back-off time has expired.

The term INFO refers to the data sent in the PADA exchange. The INFOframe (as opposed to the POLL) can have the quality that the transmitterknows the receiver will listen to it. Thus, a reason for the transmitterto fail to get an ACK to an INFO frame may bee either the INFO frame haderrors or the ACK was received in error. Each node can compute the INFOsuccess percentage (INFO %) to each of its neighbors using anexponentially weighted moving average formula. This computation canoccur whenever any INFO frame is successfully transmitted or has failed;it may not be computed on POLL failure. The link cost algorithm can usethe INFO % only due to the fact that it may better represent the linkquality between directly connected links.

The back-off algorithm can be invoked whenever a POLL or INFO framefails. A random back-off can be generated within the current back-offwindow. The current back-off window can be a geometrically increasingwindow; each consecutive failure can increase the window over which therandom back-off is rolled. Thus, lower packet transmit-successpercentages can result in greater back-offs.

The link cost can be designed to represent the total amount of time ittakes, on average, to send a PADA transaction of fixed size. In oneembodiment, this fixed size can be chosen to be 50 milliseconds. In someinstances, 50 milliseconds may be ideal since it represents a typicalpacket data size in the network. Other PADA transaction sizes areentirely feasible. This time may then be calculated for various INFO %(the POLL can be assumed to always succeed), including the averageamount of back-off time given the INFO %. This data can be kept bynetwork nodes in a look up table. The link cost to a neighbor can becalculated by looking up the PADA transaction time in the table giventhe INFO %. The table can be, for example, kept in increments of 4%.

In one embodiment, bi-directional values can be used to get the finallink cost. That is, the upstream node can send its INFO % success to thesource node. The source node then may tabulate the “average time” forboth the upstream's INFO % to it and source node's INFO % to theupstream node. This may result in a stable bi-directional route becauserouting can require a node to be able to send packets successfully bothup and down stream.

b) Path Cost Evaluation

The path cost can be calculated by adding the link costs over a path.Because the link costs can be units of time (and not INFO %) they can beadded up and do not need to be multiplied together.

Neighbor Query & Bad Neighbor List

The neighbor query can be a way for a node to quickly discover a largeset of neighbors without having to transmit discovery packets randomly.When a node discovers neighbors, it can go into an “active” neighbordiscovery period. During this time, it can ask neighbors for the nodesthat they know about. This initial inquiry may take place at a fastrate. Once the initial discovery process is stabilized and the node isin a normal operational mode (without interruptions, reboots, etc.),neighbor queries can be sent out more slowly. Also, to prevent the nodeqfrom being too unstable (growing in size, then culling etc), the nodemay not send neighbor queries if it has more than 90% of the desirednumber of nodes on its queue.

Neighbor queries may be done in a one-shot fashion. When a node receivesa neighbor query, it may return information (MAC address, hoppingsequence etc.) about its active neighbors, except for neighbors that areInterface Management Units (IMU's) (Interface Management Units are theunits mounted on water and gas meters). The IMU's may be energyconstrained, so it may not be desirable for them to be discovered andused as possible relay nodes by many meters.

There are some nodes that an inquiring node will receive in a neighborquery process that it cannot talk to. It may receive notification aboutthese unreachable nodes in multiple neighbor queries. These nodes may beplaced on the bad nodeq to prevent nodes from continuously trying totalk to neighbors it is already aware it could not talk to. Nodes mayalso be placed on the bad node list when they are removed for any reason(some examples are: repeated down-time and reboots, very poor link andpath costs, alerts from the network server and the gateway of exclusionnodes, security alerts, etc.). Nodes on the bad node list may not bere-added to a node's nodeq, unless they have rebooted and their linkconditions have been validated. The bad nodeq also helps stabilize theactual nodeq, because nodes may not be able to reacquire other nodesimmediately after they were removed. Nodes may be removed from the badnodeq after a specified period.

Nodes may also be removed from the bad nodeq if a node does not haveenough neighbors. To qualify for reinstatement into the regular nodeq,the node in the bad nodeq list may have been accessed by the reinstatingnode in the recent past and has some link information in its storage.This can assure that the node could talk to them at one time and theywould have been rediscovered in neighbor queries if they were not on thebad nodeq.

Culling

The process of culling may be to eliminate a number of neighbors from anode's nodeq before it runs out of memory to allocate node pointers.Culling may be done preemptively so that there is space fornew/disconnected nodes to connect to a particular node, and also tocontrol traffic. The choice of the number of nodes and which nodes tocull can have an impact on connectivity and network operation.

Goals of culling include:

Keep the nodeq small to minimize network congestion and interference

Keep room for new/disconnected meters on the nodeq

Cull infrequently to minimize instability

Minimize culling's impact on routing

Keep nodes with high link quality

A first step in designing the culling algorithm may be to decide thatthe optimal number of nodes in the nodeq should be 100-110 nodes (basedon traffic). The culling algorithm may have hysteresis built into it.This implies that there may be a high level and a low level of nodes onthe nodeq. Once the number of nodes exceeds the high level, node may beculled until the nodeq is at the low level.

A next step in the culling algorithm may be for the source node todecide which nodes to cull in the event that culling is required. Inorder to not disrupt the routing, the routing layer of the source nodemay mark the nodes that it is currently using as upstreams. These nodesmay not be culled. Next, nodes that are using the source node asupstreams may also not be culled. Furthermore, the source node may avoidculling infrastructure nodes since they are useful in reducing thenumber of routing hops that packets take, and also in the event ofnetwork outage. Infrastructure nodes can be relays, gateways and FieldService units (FSUs). FSUs may not be culled to enable field debug,firmware update and other maintenance functions. Each node may beinstructed to keep a certain number of gateways and relays on its nodeq(the number may be expressed as a percentage of nodeq size). Finally,when it has a route to an AP, a node may try to avoid culling nodes thathave not yet acquired routes. These nodes could potentially acquire aroute through the source node, so they should remain on the nodeq.

The algorithm may work as follows in one embodiment: Each time that Nnodes are to be culled, a total of three passes may be made through thenodeq to select nodes to cull. Each pass may select nodes according tolink quality (for example, lowest link quality in a pass gets culled).The first pass may be made if the node already has a route. If the nodedoes not have a route, it can skip the first pass and go directly to thecriteria for culling described below in the second pass. During thefirst pass a node may try to find N neighbors that already haveindependent routes (nodes not using each other as upstreams). A node mayknow which neighbors it is using, and which neighbors are using it,because those that are not using it may send it routing advertisementsevery 20 minutes. If N nodes are found during the first pass, no furtherpasses may be made and the selected nodes may be culled. In the secondpass the “have a route” constraint may be relaxed and nodes that do nothave routes may be culled. However, in this pass nodes that are sendingkeep messages may not be selected. In the third pass even nodes thatsend keep messages may be selected for culling. Ideally the third passis not reached very often as it can disrupt routing.

When an individual node is culled it may be sent a cull message to letit know that it is no longer on the nodeq. This will prevent theasymmetric situation that the culled node may still communicate with theculling node, but the culling node may no longer communicate with it dueto the fact that the culled node is no longer on the nodeq.

When a node is selected for culling, the cull sched flag may be markedand a cull message may be scheduled through the MLME scheduler. Afterthe cull message has been successfully transmitted, the designated nodemay be discarded. Occasionally, it may not be possible to transmit thecull message to the node. In that case the node may be discarded after afew retries.

Contingency Routing Schemes

Reverse Source Route

When a node has lost its network (in hold-down) or for some reasonreceives a packet from a Gateway that it is not configured for, thisnode may be unreachable. There can be methods to set up static routes tothe node, but these may be time-consuming. Further, it may be difficultto insert static routes to nodes because one may need to insert theroute in the node's routing table before one may get a confirmation fromit/talk to it.

The disclosure presented herein provides a solution to this problem.When a node receives a source-routed packet from an IP source, such as aGateway, that it does not have in its routing table, it mayautomatically configure a return route for this source IP address. ForIPv4, all the node has to do is insert the reverse source route in itsown routing information, e.g., L2 routing table and in the L3 IP routingtable. For IPv6, the situation is slightly more complex. In IPv6, nodesmay receive IP addresses by concatenating their MAC addresses (lower 64bits) with a prefix (upper 64 bits) that a node receives when it joins anetwork. Further, in order for the node to know the packet is destinedfor it, it must have the packet's destination address configured as itsown (typically in its multihome table). Thus, a node may receive apacket destined for itself (the lower 64 bits match its MAC address) andit may not have that IP address configured as its own. In the IPv6 case,there can be two steps that happen when deciding to insert a sourceroute: if the destination IP address is not configured as the node'sown, the node's multihome table is amended and a reverse route is addedto the L2 and L3 routing tables. If the destination address isconfigured for the node, a reverse route is only inserted if no otherroute back to the source IP address exists in the node's routing table.The route may only be valid for a short time (for approximately eightseconds, in one embodiment) so that the node may reply to the Gateway.In one embodiment, each time the AP sends the node a packet the routemay be reinserted even if it is not valid anymore.

Downstream Diversity Via Crumb Routes

In some exemplary embodiments, nodes may only keep routes for the accesspoint in the network. Thus they may not have any routes to other nodes.In the downstream direction, packets may be source routed by a Gateway.If they fail for a particular hop, there may be no way to forward themon (nodes may not keep routing tables for all other nodes in thenetwork.

The disclosure presented herein can provide a method to overcome thisand introduce downstream diversity. In one embodiment, nodes may insertcrumb routes into their routing tables for destinations that they areforwarding traffic for. A crumb route can be inserted into its routingtable when a node forwards a packet from a downstream source node. Theforwarding node can know the MAC address of the source node, as well asthe node immediately downstream from it that relayed the packet over thelast hop. The forwarding node can insert a layer 2 route to the sourcenode going through the immediate downstream node. Thus, when theforwarding node receives a packet destined for the original source node,it has a route to forward the packet along. In one embodiment, if a nodecould not forward a packet along the source route that was in thepacket, it may choose the crumb route. In one exemplary embodiment, whendetermining if it is unable to forward a packet, the node can hand it tothe MAC layer, and if the MAC layer could not send it within 8 secondsup to a maximum of 32 tries, it can consider the packet as unable to beforwarded. In one embodiment, nodes can store every crumb route theysee. In another embodiment, node can store two crumb routes perdestination (with newer ones replacing older ones). In one embodiment,the crumb routes can be in a first in-first-out type of queue. In oneembodiment, there may be space for 2000-3000 routes. In one embodiment,the older routes can be replaced by newer ones.

Power Management

The power management scheme can alleviate interference/congestion invery dense areas of deployment in a utility network by reducing thenodes' transmit power. In one embodiment, a plurality of the nodes maybe maintained at low power, but a few nodes may be left to operate withhigh transmit power so that they can be used as links out of the densearea without increasing number of hops for routing. Another feature ofthis scheme is that nodes can discover and adjust their power levelsautomatically without operations interference. In one embodiment thehardware can adjust its transmit power. One way that it may do this isto present a scale from 0 to 65 units on a mostly linear scale. A valueof 0 may represent, for example 23 dB, whereas a value of 65 may be 30dB on a mostly linear scale.

An exemplary power management scheme may be outlined as follows:

To detect such a situation: The source node may monitor how many nodesit culls and also can track cull messages from neighbor nodes that havegood RSSI/INFO %. The total number of nodes culled by a source node inits transmit (TX) message, and the total number of nodes culled byanother node in source node's receive (RX) message may be defined as K.If the number K is more than 100, for example, (or another configurationnumber), then the node may be in a high-density deployment. In oneembodiment, the number 100 was chosen because of typical trafficanalysis in utility networks.

After the high-density has been detected: The node may employ a randomnumber to determine how much it reduces the power. In some embodiments,the power range may be from 35 to a minimum of 1. With a percentage of1/(4K), the node may leave its power at maximum. Otherwise, if K>200, itmay choose a power level randomly in the range of 1-5. In certain othercases, the chosen value may be in the range of 5-10. Thus, after thefirst decrease, there is a possibility of a second decrease. At the endof the power decreases there may be about 2-4 nodes out of a 100 or sonodes with maximum power.

When a node increases the power: If a node has too few nodes on nodeq(<25 nodes) and has already done a “neighbor restart” where the cullednodes in the bad neighbor list have been removed and two hours havepassed to re-acquire neighbors, and a node still has <50 nodes on itsnodeq, then the node may increase the power up by 5 units.

Routing Outage Restoration

When a network node reboots, there may be a necessity to notify theutility back office server that it has rebooted after an outage event ofspecific characteristics (system-wide outage, local network outage, nodeequipment outage, other).

In order to save packets in the utility network, it may be inefficientto send a separate notification informing the back office server eachtime a node has rebooted. Instead, in the network registration, eachnode may include an element that informs the Gateway that the node hasrebooted. Along with that information, the node may inform the Gatewayabout the following:

How long it has been up

What was the nature of the outage

Whether or not it has “cleanly” or “uncleanly” rebooted

Is there a core on the node

What the core version is (if there is a core)

The information may be compiled at the Gateway for network-wide status.The Gateway may form an SNMP TRAP that may be sent to the back officeserver. Thus, the method saves network traffic and more quickly informsthe back office server that nodes in the field have gone down orrebooted.

The subject matter has been described with reference to particularembodiments. However, it will be readily apparent to those skilled inthe art that it is possible other embodiments described above. This maybe done without departing from the spirit of the claims.

Thus, the embodiments are merely illustrative and should not beconsidered restrictive in any way. The scope is given by the appendedclaims, rather than the preceding description, and all variations andequivalents which fall within the range of the claims are intended to beembraced therein.

1. A method of time synchronization in a network, comprising:requesting, by a requesting node, a current time value from a gateway asmaintained by the gateway by sending a request from the requesting nodeto the gateway inserted in a data-link interface TLV(type-length-value); responding, by the gateway to the node, with aresponse packet comprising a value corresponding to the current timevalue maintained by the gateway; at each hop from the gateway to thenode, adding a value corresponding to a transmission delay to theresponse packet at that hop; receiving, by the requesting node, theresponse packet; and based on the current time value and the addedvalues in the response packet received by the requesting node,determining, by the requesting node, a current time value to bemaintained by the requesting node and corresponding to the current timevalue maintained by the gateway.
 2. The method of claim 1, wherein therequesting node determines the current time value to be maintained bythe requesting node by adding the value corresponding to the currenttime value as maintained by the gateway in the response packet and thevalue corresponding to the transmission delay for the each hop.
 3. Themethod of claim 1, wherein each response packet including the currenttime value as maintained by the gateway is flagged to indicate that eachsuch response packet should be examined at each hop.
 4. The method ofclaim 1, wherein the requesting of time by the requesting node from thegateway is carried out by sending a request from the requesting node tothe gateway as a standalone IP packet.
 5. The method of claim 1, whereinthe requesting of the current time by the requesting node from thegateway is carried out by sending a request from the requesting node tothe gateway included in a network registration packet registering therequesting node with the gateway.
 6. The method of claim 1, wherein therequested time information sent by the gateway to the requesting node isincluded in the response packet in TLV format.
 7. The method of claim 1,wherein the requesting node and the gateway are part of afrequency-hopping spread-spectrum based wireless utility network.
 8. Amethod of power management in a network, comprising: determining whethera source node is in a high-density area of other nodes; andautomatically reducing transmit power of the source node in the eventthe determination is that the source node is in the high-density area,wherein the high-density area is determined to exist if a total numberof nodes culled by the source node as identified in transmit messages ofthe source node, and a total number of nodes culled by another nodebased on messages received by the source node, amounting to a combinedtotal of culled messages, exceeds a predetermined value, wherein cullingby the source node and the other nodes is based on a determination bythe source node and the other nodes that use of memory by the sourcenode and the other nodes to maintain neighbor relationships isexcessive.
 9. The method of claim 8, wherein the predetermined value is100.
 10. The method of claim 8, wherein the node's power is reduced to anew randomly selected power level.
 11. The method of claim 10, whereinthe randomly selected power level is in a range from about a minimum of1 to a maximum of 35 units on a scale of 0 to 65 units, wherein the 0 to65 unit scale corresponds to a range of 7 db.
 12. The method of claim10, wherein the randomly selected power level is in a range from about 1to 10 units on a scale of 0 to 65 units, wherein the 0 to 65 unit scalecorresponds to a range of 7 db, when the combined total of culledmessages is greater than
 200. 13. The method of claim 8, wherein thesource node may increase power by about 5 units on a scale of 0 to 65units, wherein the 0 to 65 unit scale corresponds to a range of 7 db,when the source node determines that there are fewer than 50 nodes in aneighbor list of the source node.
 14. A method of power management in anetwork, comprising: determining whether a source node is in ahigh-density area of other nodes; and automatically reducing transmitpower of the source node in the event the determination is that thesource node is in the high-density area, wherein the high-density areais determined to exist if a total number of nodes culled by the sourcenode as identified in transmit messages of the source node, and a totalnumber of nodes culled by another node based on messages received by thesource node, amounting to a combined total of culled messages, exceeds apredetermined value, wherein culling by the source node and the othernodes is based on a determination by the source node and the other nodesthat use of memory by the source node and the other nodes to maintainneighbor relationships is excessive, wherein the node's power is reducedto a new randomly selected power level, and wherein in an event ofadditional power reductions, the power reduction is terminated whenthere are no more than 2 nodes operating at maximum power out of 100nodes.